1. Field of the Invention
The present invention pertains generally to plasma processing and, more particularly, to a system and method for discretely controlling a plasma process over discrete areas within a system.
2. State of the Art
Many processes utilize plasma as a form of modification to chemical and physical surfaces. Such surface modifications may include etching for the removal of surface material, treatment of a surface such as through the use of a plasma enhanced chemical vapor deposition, alterations and enhancements for ion implantation or other surface modification or preparation techniques known by those of ordinary skill in the art. Plasma systems have been developed which utilize a substantial distance between the plasma and the surface of the substrate undergoing a plasma process. However, improved plasma processes prefer a close proximity of the plasma with the surface to be processed which enhances the desired chemical reactions and reduces contamination and damage to process equipment. Conventional plasma systems may bias a substrate to form an electric field near the substrate or the backing plate supporting the substrate thereby enhancing an attraction and providing control of the ion density and ion energy.
Various types of plasma sources are known by those in the art, namely capacitively coupled, electron cyclotron resonance, helicon and inductively coupled sources. These various types of plasma sources have individual benefits and shortcomings. Regarding the capacitively coupled plasma source, the RF energy is capacitively coupled into a plasma which fills the entire processing chamber. In many conventional systems, such as capacitively coupled systems, the ion density and ion energy are undesirably intrinsically coupled, and therefore cannot be desirably independently controlled. While capacitively coupled RF reactors may produce a generally uniform plasma over a many square centimeter area, the same RF which produces the plasma also generates a bias voltage between the plasma and the surface undergoing processing. Therefore, the plasma density and the ion bombardment energy generally increases with the RF power injected into the plasma system. Therefore, adjustments to the density may be made by changing the gas density and the RF power level but such adjustments are limited since the single RF source produces both a plasma and bias voltage.
Some applications require higher ion density and ion energy than may be generally produced by capacitively coupled RF reactors. Electron cyclotron resonance, helicon, and inductively coupled plasma sources may provide higher densities and energies. Such generators generally decouple or separate plasma generation from the generation of ion energy relating to the ion bombardment of the process surface. While these plasma sources may separate the control and formation of ion density and ion energy, such plasma sources lack uniformity across a particular surface area. Additionally, such approaches generate large volumes of plasma outside of the processing region and shower surrounding surfaces with ion bombardment.
The various aforementioned plasma sources and the resulting plasma generated therein are influenced by many variables including the source type, the processing chamber dimensions, the gas density and uniformity, as well as other variables known by those of ordinary skill. In order to obtain a desired plasma condition, many variables must be managed and various processes must endure processing tradeoffs. It should be apparent that as specific devices become miniaturized and the associated substrates increase in area and dimensions, there is a need to provide more uniformity for a process across an entire or majority of the surface area being processed. Additionally, there are needs for providing a controllably varied process across a substrate by managing regional or localized processes across a spatial dimension of a substrate.